JP5534834B2 - Holding pad and polishing method - Google Patents

Description

  The present invention relates to a holding pad and a polishing method, and in particular, is formed by a wet film forming method, and has a skin layer on a holding surface side for holding an object to be polished, and the holding surface from the holding surface side inside. The present invention relates to a holding pad provided with a soft plastic sheet formed with foam expanded toward the back side of the sheet and a polishing method using the holding pad.

  Conventionally, optical materials such as lenses, plane-parallel plates and reflecting mirrors, hard disk substrates, silicon wafers, glass substrates for liquid crystal displays and the like (objects to be polished) require high-precision flatness. Polishing processing using is performed. Usually, a double-side polishing machine or a single-side polishing machine is used for polishing these objects to be polished. In a single-side polishing machine that polishes the workpieces one side at a time, the workpiece is held on one side by a holding surface plate with a flat surface, and the polishing liquid is supplied by a polishing cloth attached to the polishing surface plate with a flat surface. However, polishing is performed on the other surface side (processed surface) of the object to be polished.

  Generally, in a polishing process using a single-side polishing machine, a soft cloth or the like is used on the holding surface plate in order to avoid scratches (scratches) on the surface of the object to be polished, which are caused when the object is in direct contact with a metal holding surface plate. The holding pad is installed. For example, a holding pad such as a glass substrate for a liquid crystal display has a skin layer on the holding surface side for holding an object to be polished and has a foam expanded inside from the holding surface side toward the back side of the holding surface. A soft plastic sheet in which is formed is used. This soft plastic sheet is a wet film-forming method in which a resin solution in which a soft plastic (resin) is dissolved in a water-miscible organic solvent is applied to a sheet-shaped film-forming substrate, and then the resin is coagulated and regenerated in an aqueous coagulating liquid. Manufactured by. Along with the coagulation regeneration, a skin layer is densely formed on the surface (holding surface) side of the soft plastic sheet with a thickness of about several μm, and foaming is continuously formed on the inner side of the skin layer. The soft plastic sheet formed by the wet film forming method usually has a thickness of 0.1 to 1.0 mm from the viewpoint of workability when the resin solution is applied and the resin is solidified and regenerated. Since the skin layer formed densely has a flat surface and excellent contact with the object to be polished, the object to be polished can be held. During polishing, the holding pad is mounted on the holding surface plate on the opposite side of the holding surface, and the object to be polished is held by the holding surface being in close contact with the object to be polished.

  However, in the wet film formation method, since the resin solution is viscous, thickness unevenness (variation) occurs at the time of application to the film formation substrate, and thickness variation also occurs due to the replacement of the organic solvent and the aqueous coagulation liquid during solidification regeneration. Is likely to occur. For this reason, the flatness of the holding surface of the soft plastic sheet is impaired (becomes a largely wavy surface). When holding an object to be polished with a holding pad using a soft plastic sheet with uneven thickness, the pressing force applied to the object to be polished increases at the thick part of the holding pad. An equal pressing force is not applied to the object. For this reason, the processed surface of the object to be polished is greatly polished at the portion where the thickness of the holding pad is large, and the unevenness of the thickness of the holding pad is transferred to the object to be polished, so that the flatness of the object to be polished is impaired.

  In order to reduce unevenness in the thickness of the soft plastic sheet, buffing (surface sanding) may be performed on the holding surface side after the soft plastic sheet is manufactured. Since the thickness of the skin layer is only a few μm and smaller than the thickness unevenness of the soft plastic sheet, if the buff treatment is performed to eliminate the thickness unevenness, the skin layer disappears and the foam is opened on the holding surface. Material retention is reduced. Further, when the skin layer is left, the thickness unevenness remains as it is, and it becomes difficult to improve the flatness of the object to be polished. In order to solve this problem, for example, the present inventors have disclosed a holding pad in which the back side of the holding surface of the soft plastic sheet is buffed so that the thickness of the soft plastic sheet is uniform (patent) Reference 1). In this holding pad, since the back side of the holding surface is buffed, thickness unevenness can be reduced without impairing the skin layer excellent in the ability to hold an object to be polished.

JP 2006-62059 A

  However, in the technique of Patent Document 1, since unevenness in thickness is reduced while leaving a skin layer, sufficient flatness can be expected for a conventional object to be polished. It is becoming difficult to satisfy. For example, a liquid crystal display glass substrate that employs an IPS (In-Place-Switching) drive system is superior to the flatness required for conventional objects to be polished in order to exhibit excellent characteristics with high brightness and wide viewing angle. Flatness is required. Furthermore, not only such a glass substrate for an IPS liquid crystal but also a demand for flatness of an object to be polished is increasing in various fields. Therefore, even if the soft plastic sheet has a thickness unevenness that does not cause a problem in the past, the pressing force applied to the object to be polished varies during the polishing process, and it may be difficult to ensure a high level of flatness on the object to be polished.

  An object of the present invention is to provide a holding pad that can reliably hold an object to be polished and equalize the pressing force applied to the object to be polished, and a polishing method using the holding pad. .

In order to solve the above problems, a first aspect of the present invention is formed by a wet film forming method, and has a skin layer on a holding surface side for holding an object to be polished, and the holding surface side in the inside. In the holding pad provided with the soft plastic sheet in which the expanded foam is formed toward the back side of the holding surface, the soft plastic sheet has a uniform thickness in the range of 1 mm to 2 mm. When the back side of the holding surface is buffed, the average thickness when the initial load of 100 g per 1 cm ² is applied in the thickness direction of the soft plastic sheet is X, the maximum thickness is Xmax, and the minimum thickness is Xmin in, per 1 cm ² minimum Ymin of the variation of the thickness to the average thickness X when a load is applied in addition to the initial load 100g is, satisfy the relationship Ymin ≧ Xmax-Xmin It is characterized in.

In the first aspect, since the back side of the holding surface is buffed so that the thickness of the soft plastic sheet is uniform within a range of 1 mm to 2 mm, the holding surface is substantially flat when mounted on the surface plate. As a result, the contact between the holding surface and the object to be polished is improved and the object to be polished can be securely held, and an initial load of 100 g per 1 cm ² is applied in the thickness direction of the soft plastic sheet. When the average thickness is X, the maximum thickness is Xmax, and the minimum thickness is Xmin, the minimum value Ymin of the change in thickness with respect to the average thickness X when a load of 100 g is applied per 1 cm ² in addition to the initial load is In order to satisfy the relationship of Ymin ≧ Xmax−Xmin, the thickness of the soft plastic sheet changes uniformly beyond the range of thickness variation due to the initial load during polishing. Since elasticity of stick sheet acts, it is possible to equalize the pressure exerted on the object to be polished, it is possible to improve the planarity of the polished object.

  In the first aspect, the soft plastic sheet may be made of polyurethane resin. Moreover, you may further provide the double-sided tape for attaching to a surface plate in the buffed surface side of a soft plastic sheet. At this time, at least one kind of substrate selected from a flexible film, a nonwoven fabric, and a woven fabric can be further provided between the soft plastic sheet and the double-sided tape.

Further, the second aspect of the present invention is formed by a wet film-forming method, and has a skin layer on the holding surface side for holding an object to be polished, and the back surface of the holding surface from the holding surface side inside. A polishing method for polishing the object to be polished, which is held by a holding pad provided with a soft plastic sheet having a foam expanded in diameter toward the side, wherein the soft plastic sheet has a thickness of 1 mm to The back side of the holding surface is buffed so as to be uniform within a range of 2 mm, and the average thickness when an initial load of 100 g per 1 cm ² is applied in the thickness direction of the soft plastic sheet is X, Xmax the maximum thickness, the minimum thickness is taken as Xmin, the minimum value Ymin the thickness to the average thickness X amount of change when applying a load of 100g in addition to the initial load per 1 cm ^2, Y in ≧ Xmax−Xmin, the holding pad is mounted on a surface plate on the opposite side of the holding surface, and the surface to be polished is held in close contact with the holding surface. Polishing the other side of the object.

According to the present invention, since the back surface side of the holding surface is buffed so that the thickness of the soft plastic sheet is uniform in the range of 1 mm to 2 mm, the holding surface is substantially flat when mounted on the surface plate. As a result, the contact between the holding surface and the object to be polished is improved and the object to be polished can be securely held, and an initial load of 100 g per 1 cm ² is applied in the thickness direction of the soft plastic sheet. When the average thickness is X, the maximum thickness is Xmax, and the minimum thickness is Xmin, the minimum value Ymin of the change in thickness with respect to the average thickness X when a load of 100 g is applied per 1 cm ² in addition to the initial load is In order to satisfy the relationship of Ymin ≧ Xmax−Xmin, the thickness of the soft plastic sheet changes uniformly beyond the range of thickness variation due to the initial load during polishing. Since elasticity of stick sheet acts, it is possible to equalize the pressure exerted on the object to be polished, it is possible to improve the flatness of the object to be polished, the effect can be obtained as.

It is sectional drawing which shows typically the holding pad of embodiment which concerns on this invention. It is process drawing which shows the outline of the manufacturing process of the holding pad of embodiment. It is sectional drawing which shows typically the state change of the polyurethane sheet in a buff processing process, (A) is a state when it forms in a film-forming base material, (B) is when a holding surface is press-contacted to a press-contact roller. State (C) shows the state when the pressure roller is removed after buffing. It is sectional drawing which shows the state when a to-be-polished object closely_contact | adheres to a holding pad, (A) is a state before a holding pad contacts a to-be-polished object, (B) is a holding pad to a to-be-polished object. A state where the pressing force applied to the object to be polished is equalized is shown. It is sectional drawing which shows the state when a to-be-polished object adheres to the conventional holding pad typically, (A) is a state before a holding pad contacts a to-be-polished object, (B) is a holding pad being to-be-polished. Each shows a state in which the pressing force applied to the object being in contact with the object varies.

  Embodiments of a holding pad according to the present invention will be described below with reference to the drawings.

(Holding pad)
As shown in FIG. 1, the holding pad 10 of this embodiment includes a polyurethane sheet 2 as a soft plastic sheet that is formed of a polyurethane resin by a wet film forming method and has a holding surface P for holding an object to be polished. Yes.

  The polyurethane sheet 2 has a dense skin layer 2a on the holding surface P side, and has a foam layer 2b on the inside (inside the skin layer 2a). In the foam layer 2b, a foam 3 having a triangular shape with a rounded length along the thickness direction is formed over the entire length of the polyurethane sheet 2. The foam 3 is formed so that the hole diameter on the holding surface P side is smaller than the back surface (lower surface in FIG. 1) side of the holding surface P. That is, the diameter of the foam 3 is increased from the holding surface P side toward the back side of the holding surface P. In the polyurethane resin between the foams 3, foam (not shown) having a pore diameter smaller than that of the foam 3 on the skin layer 2 a side is formed. That is, the polyurethane resin of the foam layer 2b has a microporous structure. The foam 3 of the foam layer 2b and the foam (not shown) are connected in a mesh pattern through communication holes (not shown).

The polyurethane sheet 2 is buffed so that the thickness of the polyurethane sheet 2 (length in the vertical direction in FIG. 1) is uniform within the range of 1 to 2 mm on the back side of the holding surface P (details will be described later). . For this reason, the foam 3 and a part of the foam (not shown) are opened on the back surface of the holding surface P. Since the diameter of the foam 3 is increased on the back side of the holding surface P, the average aperture diameter is 250 μm or more on the back side of the holding surface P. In the polyurethane sheet 2, the average thickness when the initial load of 50 to 200 g is applied per 1 cm ^{2 in the} thickness direction is X (mm), the maximum thickness is Xmax (mm), and the minimum thickness is Xmin (mm). Show. When the polyurethane sheet 2 is subjected to a load of 100 g (initial load + 100 g) in addition to the initial load, the minimum value Ymin (mm) of the change in thickness with respect to the average thickness X satisfies the relationship of Ymin ≧ Xmax−Xmin. It has been adjusted to meet. In other words, the amount of change in the thickness of the polyurethane sheet 2 when a load of 100 g is applied in addition to the initial load becomes larger than the thickness variation range due to the initial load alone.

  The holding pad 10 has a base material 6 that supports the polyurethane sheet 2 bonded to the back side of the holding surface P. As the substrate 6, at least one selected from a flexible film such as a film made of polyethylene terephthalate (hereinafter abbreviated as PET), a nonwoven fabric, or a woven fabric is used. The other surface side of the double-sided tape 7 for attaching the holding pad 10 to the polishing machine having the release paper 8 on one surface side (lowermost surface side) is attached to the lower surface side (the side opposite to the polyurethane sheet 2) of the base material 6. Are combined.

(Manufacture of holding pads)
The holding pad 10 is manufactured through each process shown in FIG. First, in the preparation step, N, N-dimethylformamide (hereinafter abbreviated as DMF), which is a water-miscible organic solvent capable of dissolving polyurethane resin, and an additive are mixed to dissolve the polyurethane resin. The polyurethane resin has a 100% modulus of the resin of 20 MPa or less, and is selected from polyester, polyether, polycarbonate, and the like. For example, the polyurethane resin is dissolved in DMF so that the polyurethane resin becomes 30% by weight. Let As the additive, a pigment such as carbon black, a hydrophilic activator that promotes foaming, and a hydrophobic activator that stabilizes the coagulation regeneration of the polyurethane resin are used in order to control the size and amount (number) of foam 3. be able to. The obtained solution is degassed under reduced pressure to obtain a polyurethane resin solution. At this time, the thickness of the obtained polyurethane sheet can be adjusted so as to satisfy the above-described relational expression by adjusting the resin concentration and the additive composition.

  In the coating process, coagulation regeneration process, and washing / drying process, the polyurethane resin solution obtained in the preparation process is continuously applied to the film-forming substrate and immersed in an aqueous coagulation solution to coagulate and regenerate the polyurethane resin, followed by washing. Thereafter, the polyurethane sheet 2 is obtained by drying. In this example, the coating process, the coagulation regeneration process, and the washing / drying process consist of a coagulation tank filled with coagulation liquid for coagulating and regenerating the polyurethane resin based on water, which is a poor solvent for the polyurethane resin, and coagulation regeneration. It is continuously executed in a film forming apparatus continuously provided with a cleaning tank filled with a cleaning solution such as water for cleaning the polyurethane resin and a cylinder dryer for drying the polyurethane resin.

  As shown in FIG. 2, in the coating process, the polyurethane resin solution prepared in the preparation process is coated on the film forming substrate substantially uniformly by a coating device such as a knife coater at room temperature. At this time, in order to make the final (buffed) polyurethane sheet 2 have a thickness of 1 to 2 mm, polyurethane is adjusted by adjusting a gap (clearance) between the coating apparatus and the upper surface of the film forming substrate. It is preferable to set the coating thickness of the resin solution to about 1.0 to 2.3 mm. In this example, a flexible film made of PET or the like into which the coagulation liquid does not penetrate is used as the film forming substrate.

  In the coagulation regeneration process, the polyurethane resin solution applied to the film forming substrate is guided into the coagulation liquid in the coagulation tank. In the coagulation liquid, first, a skin layer 2a having a thickness of several μm is formed on the surface of the applied polyurethane resin solution. Thereafter, the polyurethane resin coagulates and regenerates on one side of the film-forming substrate as the substitution of DMF in the polyurethane resin solution and the coagulating liquid (water) proceeds. When DMF removes the solvent from the polyurethane resin solution, foam 3 is formed in the polyurethane resin. At this time, since water does not penetrate into the film-forming substrate of the PET film, desolvation occurs on the surface of the polyurethane resin solution (skin layer 2a), and foam 3 having a larger pore diameter on the film-forming substrate side than the surface side is formed. Is done. The coagulated and regenerated polyurethane resin is pulled up from the coagulating liquid, conveyed to a cleaning tank, and guided into the cleaning liquid.

  Here, formation of the foam 3 of the polyurethane sheet 2 will be described. DMF used for dissolving the polyurethane resin is a solvent generally used for dissolving the polyurethane resin, and can be mixed in an arbitrary ratio with respect to water. For this reason, in the production of the polyurethane sheet 2, when the polyurethane resin solution is immersed in the coagulation liquid, first, substitution of DMF and coagulation liquid (coagulation regeneration of the polyurethane resin) occurs on the surface of the polyurethane resin solution to form the skin layer 2a. . Thereafter, since the coagulating liquid enters the polyurethane resin solution from the portion where the skin layer 2a easily enters, a portion where the substitution of the DMF and the coagulating solution proceeds rapidly and a portion where it delays are generated, and a relatively large foam 3 is formed. Is done. That is, the replacement of DMF with the coagulating liquid occurs through the skin layer 2a. Since a film made of PET that does not penetrate the coagulation liquid is used as the film formation substrate, DMF elutes only from the surface side (skin layer 2a side) of the polyurethane resin solution, and foam 3 is greatly rounded on the film formation substrate side. It becomes a round cone shape.

  In the washing / drying step, the polyurethane resin is washed by eluting DMF remaining inside from the polyurethane resin guided in the washing liquid. After washing, the polyurethane resin is pulled up from the washing solution and the excess washing solution is squeezed out. Thereafter, the polyurethane resin is dried by passing it through a cylinder dryer having a cylinder having a heat source therein along the peripheral surface of the cylinder. The dried polyurethane resin (polyurethane sheet 2) is taken up together with the film-forming substrate.

  In the buffing process, buffing is performed on the back side of the holding surface P of the polyurethane sheet 2 after drying. As shown in FIG. 3A, the wound polyurethane sheet 2 is formed on a PET film-forming substrate. Since the thickness of the polyurethane sheet 2 varies during film formation, the holding surface P is uneven. After the film-forming substrate is peeled off, as shown in FIG. 3B, the holding surface P is flattened by pressing the surface of the pressing roller 65 with a flat surface against the holding surface P. Unevenness appears on the back surface Q1 side. Unevenness appearing on the back Q1 side is removed by buffing. In this example, since the continuously manufactured polyurethane sheet 2 has a band shape, the back surface Q1 side is continuously buffed while the pressure roller 65 is pressed against the holding surface P. As a result, as shown in FIG. 3C, the back surface Q1 side is buffed to form a substantially flat back surface Q, and the thickness variation of the polyurethane sheet 2 is eliminated. Note that in FIG. 3C, the holding surface P and the back surface Q are shown flat for easy understanding, but the polyurethane sheet 2 has a thickness of 1 to 2 mm on both surfaces of the polyurethane sheet 2 alone. It has unevenness that becomes uniform, and the holding surface P becomes substantially flat when the substrate 6 is bonded together or attached to a polishing machine.

  As shown in FIG. 2, in the laminating process, the base material 6 is bonded to the buffed surface (back surface Q) side of the polyurethane sheet 2. The other surface side of the double-sided tape 7 having the release paper 8 attached on one side is bonded to the surface of the base 6 opposite to the polyurethane sheet 2. Then, after cutting into a desired shape such as a circle, an inspection such as confirming that there is no adhesion of dirt or foreign matter is performed to complete the holding pad 10.

(Polishing)
When polishing the object to be polished with the obtained holding pad 10, for example, the holding pad 10 is attached to the holding surface plate of a single-side polishing machine with the double-sided tape 7 from which the release paper 8 has been peeled, and is polished on the polishing surface plate. Put on the pads. Both the surface on which the holding pad 10 of the holding surface plate is mounted and the surface on which the polishing pad of the polishing surface plate is mounted are formed flat. For this reason, the holding pad 10 forms a substantially flat holding surface P by being mounted on the holding surface plate. The object to be polished is held on the holding surface plate by bringing it into close contact with the holding surface P of the holding pad 10 on the opposite side of the processing surface. At this time, since the surface tension of the water that has entered the skin layer 2a acts by spraying a small amount of water on the holding surface P and pressing the object to be polished, the object to be polished is held on the holding surface P. At the time of polishing, a polishing liquid containing abrasive particles is supplied between the processing surface of the object to be polished and the polishing pad, and the processing surface side is polished with the polishing pad while applying polishing pressure.

(Function)
Next, the operation and the like of the holding pad 10 of this embodiment will be described.

  In the holding pad 10 of this embodiment, the back side of the holding surface P is buffed so that the thickness of the polyurethane sheet 2 is uniform within a range of 1 to 2 mm. For this reason, since the thickness of the polyurethane sheet 2 is uniform while leaving the skin layer 2a having excellent retention of the object to be polished, the surface of the skin layer 2a by attaching the holding pad 10 to the holding surface plate, that is, The holding surface P becomes substantially flat, and the contact between the holding surface P and the object to be polished can be improved. By bringing the object to be polished into close contact with the holding surface P, the object to be polished is securely held substantially flat, so that the flatness of the processed surface of the object to be polished can be improved by polishing.

In addition, in the holding pad 10 of the present embodiment, when a load of 100 g (initial load + 100 g) is applied in addition to the initial load per 1 cm ² in the thickness direction of the polyurethane sheet 2, the initial load is applied. The minimum value Ymin (mm) of the thickness variation with respect to the average thickness X is adjusted so as to satisfy the relationship of Ymin ≧ Xmax−Xmin. At the time of polishing processing, a polishing pressure of 10 to 300 g per cm ² is applied to the object to be polished. Therefore, in the polyurethane sheet 2 in which the foam 3 is formed inside, the polishing pressure is applied, and it is uniform within a range of 1 to 2 mm. The elasticity of the uniform thickness changes uniformly beyond the thickness variation range due to the initial load. For this reason, since the elasticity of the polyurethane sheet 2 acts on the object to be polished in addition to the polishing pressure by holding the object to be polished in close contact with the holding surface P, the polyurethane sheet 2 after buffing has a slight thickness. Even if the spots remain, the pressing force applied to the object to be polished during the polishing process can be equalized. Specifically, as shown in FIG. 4 (A), even if the polyurethane sheet 2 is buffed, some thickness spots may remain on the holding pad 10. In this case, the holding surface P comes into contact with the object 70 with slight undulation, and a polishing pressure (arrow a) is applied during the polishing process. As shown in FIG. 4B, since the polyurethane sheet 2 is compressed by the polishing pressure, the elasticity of the polyurethane sheet 2 acts in addition to the polishing pressure, so that the pressing force (arrow b) applied to the object to be polished is Equalized. As a result, even when polishing a glass substrate for IPS liquid crystal or a large object to be polished that requires high-precision flatness, the object to be polished that is held approximately flat is pressed almost evenly and the processed surface is polished. Therefore, the flatness of the processed surface can be improved. When the minimum value Ymin of the amount of change in thickness is smaller than the thickness variation range due to the initial load, that is, when Ymin <Xmax−Xmin, the thickness change occurs when the polyurethane sheet 2 is compressed with the polishing pressure. In the amount, the uneven thickness at the initial load is not absorbed. For this reason, there is a possibility that it becomes difficult to hold the object to be polished using the entire surface of the polyurethane sheet 2, and the elasticity of the polyurethane sheet 2 becomes locally insufficient even when a polishing pressure is applied during the polishing process. It becomes difficult to equalize the pressing force applied to the object.

  Furthermore, in the holding pad 10 of the present embodiment, the thickness of the polyurethane sheet 2 after the buffing process is in the range of 1 to 2 mm, so that the coating thickness of the polyurethane resin solution is 1.0 in the coating process during wet film formation. Set to ~ 2.3 mm. If the thickness after buffing is less than 1 mm, it is difficult to exhibit sufficient elasticity during polishing. When the coating thickness in the coating process exceeds 2.3 mm, it becomes difficult to sufficiently solidify and regenerate the polyurethane resin to the inside during wet film formation. In this case, although sufficient coagulation regeneration can be expected by lengthening the coagulation regeneration time, it is not preferable because the thickness unevenness may be increased during the coagulation regeneration. Moreover, in the holding pad 10 of this embodiment, since the average opening diameter of the hole formed in the back surface (buffed surface) of the holding surface P of the polyurethane sheet 2 by buffing is 250 μm or more, the polyurethane pad 2 is used. The absorption function of thickness spots can be enhanced and the pressing force applied to the object to be polished can be equalized. When the average opening diameter is smaller than 250 μm, the amount of change in the thickness of the polyurethane sheet 2 is small and is not easily deformed. Therefore, the adhesion between the holding surface P and the object to be polished is impaired, and the pressing force applied to the object to be polished is reduced. Variation will occur. On the other hand, if the average aperture diameter exceeds 800 μm, the amount of change in thickness when polishing pressure is applied becomes too large and the durability is lowered, so the average aperture diameter should not exceed 800 μm. Is preferred.

  Furthermore, in the holding pad 10 of this embodiment, the polyurethane sheet 2 produced by the wet film-forming method is used. In the polyurethane resin, the foam layer 3 of the skin layer 2a and the foamed layer 2b can be easily formed by wet film formation, so that it is possible to obtain the polyurethane sheet 2 in which the amount of change in thickness satisfies the relational expression described above. it can.

  Furthermore, in the holding pad 10 of this embodiment, a PET film substrate 6 is bonded to the back side of the holding surface P of the polyurethane sheet 2. For this reason, since the polyurethane sheet 2 is supported by the base material 6, handling at the time of conveyance of the holding pad 10 or attachment to a single-side polishing machine can be facilitated. Moreover, since the double-sided tape 7 is bonded to the opposite surface side of the base material 6 to the polyurethane sheet 2, the double-sided tape 7 can be easily attached to the holding surface plate.

  In the conventional wet film forming method used for manufacturing the holding pad, when the polyurethane resin solution is applied to the film forming base material, there are variations in the conveyance speed, fluctuations in the coating apparatus, and the like, resulting in variations in the coating thickness. Since the polyurethane resin is coagulated and regenerated in this state, thickness spots remain on the obtained polyurethane sheet. Moreover, in the coagulating liquid, variation occurs in the solvent removal accompanying coagulation regeneration, so that the thickness unevenness of the polyurethane sheet increases. In the holding pad using the polyurethane sheet in which the thickness unevenness is generated, the pressure applied to the object to be polished is increased in the thick part, so that the processed surface of the part is greatly polished and the flatness is impaired. The surface of the holding pad is buffed to reduce such thickness unevenness, but the thickness of the skin layer is smaller than the thickness unevenness of the polyurethane sheet. Since the skin layer effective for holding disappears, the holding property of the object to be polished is lowered. If the skin layer is left, the thickness unevenness of the polyurethane sheet remains as it is, so that the flatness of the processed surface of the object to be polished is impaired. In addition, in the wet film formation of a polyurethane sheet, the thickness is adjusted to 0.1 to 1.0 mm from the viewpoint of film forming workability. In the conventional holding pad 20 using this polyurethane sheet, as shown in FIG. 5 (A), the holding surface is greatly wavy due to the uneven thickness of the polyurethane sheet. A polishing pressure (arrow a) is applied in contact with the workpiece 70. As shown in FIG. 5B, since the thickness of the polyurethane sheet used for the holding pad 20 is 0.1 to 1.0 mm, the amount of change in thickness is limited by the thickness even when polishing pressure is applied during polishing. Therefore, the elasticity of the polyurethane sheet does not act sufficiently, and the object to be polished is less likely to adhere to the holding surface due to the occurrence of thickness spots. For this reason, the pressing force (arrow b) applied to the object to be polished varies, and the flatness of the processed surface of the object to be polished is impaired. The present embodiment is a holding pad that can solve these problems.

Although not particularly mentioned in the present embodiment, when the load of 100 g is applied in addition to the initial load per 1 cm ² in the thickness direction of the polyurethane sheet 2, The maximum value Ymax (mm) is preferably smaller than the thickness of the workpiece. In other words, the holding pad 10 can be suitably used for polishing a workpiece having a thickness larger than the maximum value Ymax of the thickness variation. In an object to be polished having a thickness smaller than the maximum thickness change value Ymax, a part of the object to be polished is excessively submerged in the polyurethane sheet 2 at the time of polishing, so that the entire surface of the object to be polished is uniformly polished. Becomes difficult.

  Further, in the holding pad 10 of the present embodiment, an example is shown in which the back surface Q1 side is continuously buffed while the pressure roller 65 is pressed against the holding surface P in the buffing process, but the present invention is limited to this. It is not a thing. For example, after the polyurethane sheet 2 is cut into a desired size, a flat plate having a flat surface may be pressed against the holding surface P to buff the back surface Q1 side.

  Furthermore, in this embodiment, although the example which bonds the base material 6 of a PET film on the back surface Q side buff-processed of the polyurethane sheet 2 was shown, this invention is not limited to this, For example, a nonwoven fabric Alternatively, a base material 6 may be used. The double-sided tape 7 may be directly bonded without bonding the substrate 6. In addition, the polyurethane sheet 2 can be used for polishing as it is without attaching the substrate 6 and the double-sided tape 7 together. In this case, an adhesive or a double-sided tape may be used when mounting on a holding surface plate of a single-side polishing machine.

  Furthermore, in this embodiment, although the example which uses the film made from PET for the film-forming base material 43 was shown, this invention is not limited to this, For example, you may use a nonwoven fabric and a woven fabric. . In this case, since it is difficult to peel off the film-forming substrate 43 after the polyurethane resin is solidified and regenerated, the surface of the film-forming substrate 43 opposite to the polyurethane resin may be buffed. Moreover, the film-forming base material 43 of a nonwoven fabric or a woven fabric may be used as the base material 6 as it is, and another base material 6 may be bonded together.

  Furthermore, in the present embodiment, the polyurethane resin is exemplified as the material of the polyurethane sheet 2, but the present invention is not limited to this. For example, a polyester resin or the like may be used, but if a polyurethane resin is used, the skin layer 2a can be easily formed by a wet film forming method. Moreover, in this embodiment, although the example which uses the polyurethane resin whose 100% modulus of resin is 20 Mpa or less was shown, this invention is not restrict | limited to this and uses the polyurethane resin whose 100% modulus exceeds 20 Mpa. Is also possible. In this case, by adjusting the size and shape of the foam 3, that is, by adjusting the ratio of the additive or the like blended in the polyurethane resin solution, the same performance as that of the polyurethane resin having a 100% modulus of 20 MPa or less is obtained. Can do. Furthermore, although the example which melt | dissolves a polyurethane resin in DMF so that it may become 30 weight% was shown, this invention is not limited to this, It changes suitably by the viscosity of a polyurethane resin solution, the thickness of the polyurethane sheet 2, etc. May be.

  In this embodiment, the knife coater is exemplified for application of the polyurethane resin solution. However, for example, a reverse coater, a roll coater, or the like may be used. There is no particular limitation. In the present embodiment, the cylinder dryer is exemplified for drying the polyurethane resin. However, the present invention is not limited to this, and for example, a hot air dryer or the like may be used.

  Further, in the present embodiment, the wet-formed polyurethane sheet 2 is buffed on the back side of the holding surface P by a buffing machine or the like, but the buffing amount is the difference between the maximum thickness and the minimum thickness of the polyurethane sheet 2. It is desirable to make it twice or more. Various materials such as sandpaper and diamond buffol are used in the buffing, but any can be used as long as uniform processing (grinding removal) is possible. At this time, the higher the buff count (number indicating the roughness of the abrasive grains), the more fine the abrasive grains can be ground and the uniform buffing process can be performed. Furthermore, the thickness accuracy is improved by buffing with a low buff count (rough abrasive grains) at the first time, and buffing with a buff count higher than the first time with a lower buff count. It can also be raised.

  Hereinafter, examples of the holding pad 10 manufactured according to the present embodiment will be described. The holding pad of the comparative example manufactured for comparison is also shown.

Example 1
In Example 1, a polyester MDI (diphenylmethane diisocyanate) polyurethane resin having a 100% modulus of 10 MPa was used as the polyurethane resin. To 100 parts of DMF solution containing 30% by weight of this polyurethane resin, 45 parts of DMF for viscosity adjustment, 40 parts of DMF dispersion containing 30% of pigment carbon black, and 2 parts of hydrophobic activator were mixed. Thus, a polyurethane resin solution was prepared. When applying the polyurethane resin solution, the clearance of the coating apparatus was set to 1.3 mm. The holding pad 10 of Example 1 was manufactured by buffing the polyurethane sheet 2 using a sandpaper of buff count # 180 with a buff treatment amount of 0.20 mm. The coating weight of the polyurethane resin solution in terms of weight per unit area of the polyurethane sheet 2 is 1072g / ^{m 2} (solid terms 252 g / ^{m 2).}

(Example 2)
In Example 2, the holding pad 10 of Example 2 was manufactured in the same manner as in Example 1 except that the clearance was set to 1.5 mm when the polyurethane resin solution was applied and the buff treatment amount was 0.25 mm.

(Example 3)
In Example 3, the holding pad 10 of Example 3 was manufactured in the same manner as in Example 1 except that the clearance was set to 2.0 mm when the polyurethane resin solution was applied.

(Comparative Example 1)
In Comparative Example 1, the holding pad of Comparative Example 1 was manufactured in the same manner as in Example 1 except that the clearance was set to 0.9 mm when the polyurethane resin solution was applied. That is, Comparative Example 1 is a holding pad having a polyurethane sheet thickness of less than 1 mm.

(Comparative Example 2)
In Comparative Example 2, a holding pad of Comparative Example 2 was produced in the same manner as Comparative Example 1 except that the polyurethane sheet was not buffed. That is, Comparative Example 2 is a conventional holding pad using a polyurethane sheet in which the thickness variation during wet film formation remains.

(Physical property evaluation 1)
About the polyurethane sheet produced by each obtained Example and the comparative example, the surface buffed was observed with the scanning electron microscope (SEM), and the hole diameter was measured. For the measurement, SEM image analysis software (manufactured by Olympus Soft-Imaging Solutions, “Scandium”) was used to determine the average pore size. The measurement results of the average pore diameter are shown in Table 1 below. In Comparative Example 2, measurement was not performed because buffing was not performed.

(Physical property evaluation 2)
About the holding pad manufactured by each Example and the comparative example, the thickness of the polyurethane sheet was measured according to the thickness measuring method described in Japanese Industrial Standard (JIS K6505). That is, the sheet thickness was measured when a load of 100 g per 1 cm ² was applied (added) to the polyurethane sheet as the initial load in the thickness direction. For the measurement of sheet thickness, a polyurethane sheet measuring 1 m in length and 1 m in width is cut into 100 pieces of 10 cm in length and 10 cm in width, and the thickness of the four corners and the center of each piece is minimized using a dial gauge (minimum scale 0.01 mm). The reading was measured up to 1 / 10th (0.001 mm) of the scale, and the average value of 5 points was defined as the thickness of one piece. The average thickness X of the sheet was the average thickness measured for 100 pieces. Further, the maximum value and the minimum value were extracted from the measured values for 100 pieces, and the maximum value and the minimum thickness were respectively determined as the maximum thickness Xmax and the minimum thickness Xmin, that is, Xmax−Xmin was determined as the thickness variation range. Furthermore, about 100 pieces cut out, the load when 100 g was added to the initial load at the same position as the position where the initial load was applied, that is, the thickness when a load of 200 g per 1 cm ² was applied was measured in the same manner. The difference between the average thickness X when the initial load was applied and the thickness of each piece when the load of 200 g / cm ² was applied was taken as the amount of change in thickness, and the minimum value Ymin and maximum value Ymax were determined. In other words, the piece having the largest thickness when a load of 200 g / cm ² is applied shows the minimum value Ymin of the thickness change amount. The results of thickness and thickness variation are shown in Table 1 below.

As shown in Table 1, in the polyurethane sheet used for the holding pad of Comparative Example 1, the average hole diameter of the buffed surface was 226.0 μm, and the size was less than 250 μm. Moreover, in Comparative Example 1 and Comparative Example 2, the thickness variation ranges (Xmax−Xmin) measured at a load of 100 g / cm ² (initial load) were 0.026 mm and 0.049 mm, respectively, and the minimum value of the thickness variation amount Ymin was 0.023 mm and 0.018 mm, respectively. That is, in both Comparative Example 1 and Comparative Example 2, the minimum value Ymin of the thickness change amount is smaller than the thickness variation range due to the initial load, and the relationship of Ymin <Xmax−Xmin is established. For this reason, when compressing by applying a load of 100 g in addition to the initial load per 1 cm ² , the thickness variation at the initial load cannot be absorbed in the thickness change amount, and the entire surface of the polyurethane sheet is used. There is a risk that the object to be polished cannot be held. Therefore, in the holding pads of Comparative Example 1 and Comparative Example 2, the thickness change amount when a load is applied to the polyurethane sheet is small, and the elasticity of the polyurethane sheet does not sufficiently act even when polishing pressure is applied during polishing processing. Variations occur in the pressing force applied to the object to be polished, and improvement in the flatness of the object to be polished cannot be expected.

On the other hand, in the polyurethane sheet 2 used for the holding pad of Examples 1 to 3, the average hole diameters of the buffed surfaces are 273.4 μm, 311.0 μm, 389.2 μm, respectively, and all are 250 μm. The size exceeded. In Examples 1 to 3, the thickness variation ranges (Xmax−Xmin) when an initial load is applied are 0.032 mm, 0.033 mm, and 0.039 mm, respectively, and the minimum value Ymin of the thickness change amount Of 0.037 mm, 0.054 mm, and 0.075 mm, respectively. That is, in each of the polyurethane sheets 2 of Examples 1 to 3, the minimum value Ymin of the thickness change amount is smaller than the thickness variation range due to the initial load, and the relationship of Ymin ≧ Xmax−Xmin is satisfied. Become. For this reason, when compressing by applying a load of 100 g per cm ² in addition to the initial load, the thickness variation at the initial load can be absorbed in the thickness change amount, and the entire surface of the polyurethane sheet 2 is used. This makes it possible to hold the object to be polished. Therefore, since the elasticity of the polyurethane sheet 2 also acts during polishing, it can be expected to equalize the pressing force applied to the object to be polished and improve the flatness of the object to be polished.

(Polishing performance evaluation)
Using the holding pads of each Example and Comparative Example, a glass substrate for liquid crystal display (470 mm × 370 mm × 0.7 mm) was polished under the following polishing conditions, and the polishing performance was evaluated. In this evaluation, the flatness a was measured from the wave center waviness by a method in accordance with Japanese Industrial Standard (JIS B0601: '82). In the measurement of the flatness a, a surface roughness shape measuring machine (manufactured by Tokyo Seimitsu Co., Ltd., Surfcom 480A) was used, and the measurement conditions shown below were set. From the measurement curve obtained due to the irregularities on the surface of the glass substrate after polishing, the width W between the adjacent convex portion (peak portion) and the convex portion, and the height between the convex portion and the concave portion (valley) After calculating the thickness S, a scatter diagram was created with the width W as the horizontal axis and the height S as the vertical axis. From the obtained scatter diagram, an approximate straight line of the primary expression S = aW was obtained, and the inclination a was defined as the final flatness a after polishing. In general, the higher the flatness, the larger the width W and the smaller the height S. Therefore, the smaller the inclination a, the better the flatness. The measurement results of the flatness a are shown in Table 2 below.
(Polishing conditions)
Polishing machine used: Oscar polishing machine (SP-1200, manufactured by Speed Fam Co., Ltd.)
Polishing speed (rotation speed): 61 rpm
Processing pressure: 76 gf / cm ²
Slurry: Cerium slurry Polishing time: 30 min
(Filter center swell measurement conditions)
Evaluation length: 90mm
Measurement speed: 3.0 mm / s
Cut-off value: 0.8-8.0mm
Filter type: 2RC
Measurement range: ± 40.0μm
Tilt correction: Spline

  As shown in Table 2, in the polishing process using the holding pads of Comparative Example 1 and Comparative Example 2, the flatness a of the processed glass substrate was 0.007 and 0.011, respectively. On the other hand, in the polishing process using each holding pad 10 of Examples 1 to 3, the flatness a is 0.003 to 0.004, both of which are superior to Comparative Example 1 and Comparative Example 2. The results are shown. Therefore, in the case of the holding pad 10 of Examples 1 to 3, the pressing force applied to the object to be polished can be equalized by the elasticity of the polyurethane sheet 2 during the polishing process. For this reason, the object to be polished held by the holding pad 10 with improved thickness accuracy is polished under a substantially uniform pressing force, so that the flatness of the object to be polished can be improved.

  The present invention contributes to the manufacture and sale of holding pads in order to provide a holding pad that can hold the object to be polished reliably and equalize the pressing force applied to the object to be polished and a polishing method using the holding pad. Therefore, it has industrial applicability.

P Holding surface Q Back surface 2 Polyurethane sheet (soft plastic sheet)
2a Skin layer 2b Foam layer 3 Foam 10 Holding pad

Claims (5)

Formed by a wet film formation method, a foam layer is formed in which a skin layer is provided on the holding surface side for holding an object to be polished and the diameter is expanded from the holding surface side toward the back side of the holding surface. In the holding pad provided with the soft plastic sheet, the back side of the holding surface is buffed so that the thickness of the soft plastic sheet is uniform within a range of 1 mm to 2 mm, and the thickness of the soft plastic sheet is When the average thickness when an initial load of 100 g per cm ² is applied in the vertical direction is X, the maximum thickness is Xmax, and the minimum thickness is Xmin, a load of 100 g was applied per cm ² in addition to the initial load. A holding pad, wherein a minimum value Ymin of a change in thickness with respect to the average thickness X at the time satisfies a relationship of Ymin ≧ Xmax−Xmin.   The holding pad according to claim 1, wherein the soft plastic sheet is made of polyurethane resin.   The holding pad according to claim 1 or 2, further comprising a double-sided tape for mounting on a surface plate on the buffed surface side of the soft plastic sheet.   The holding pad according to claim 3, further comprising at least one substrate selected from a flexible film, a nonwoven fabric, and a woven fabric between the soft plastic sheet and the double-sided tape. Formed by a wet film formation method, a foam layer is formed in which a skin layer is provided on the holding surface side for holding an object to be polished and the diameter is expanded from the holding surface side toward the back side of the holding surface. A polishing method for polishing the object held by a holding pad provided with a soft plastic sheet, wherein the soft plastic sheet has a uniform thickness in a range of 1 mm to 2 mm. The back side of the holding surface is buffed, the average thickness when an initial load of 100 g per cm ² is applied in the thickness direction of the soft plastic sheet is X, the maximum thickness is Xmax, and the minimum thickness is Xmin. when the minimum value Ymin of the variation of the thickness to the average thickness X when applying a load of 100g in addition to the initial load per 1 cm ² is of Ymin ≧ Xmax-Xmin It meets the engagement,
Attach the holding pad to the surface plate on the opposite side of the holding surface,
Polishing the other surface side of the object to be polished while holding one surface of the object to be adhered to the holding surface;
A polishing method comprising steps.

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